Digestive system and metabolism Flashcards
What are the accessory digestive organs
teeth, tongue, salivary glands, gallbladder, pancreas
Mesentary components
mesothelium, areolar tissue, mesothelium sandwich
Major layers of GI
mucosa, submucosa (vessels, glands), muscularis externa, serosa or adventitia
Mesentary
double sheet of peritoneal membrane, route for blood vessels, nerves and lymphatic vessels, stabilizes attached organs, prevents tangling
Discribe the histology of a single circular fold
covered in vili (mucosal projections),
lamina propria : next is a layer of areolar tissue that also has blood, nerve endings, lymph vessels, smooth muscle cells, lymphoid tissue
Then, submucosal plexus, a nerve network.
Then the muscular mucosae is two layers of smooth muscle, this inner is circular, outer is longitudinal. A myenteric plexus is between.
Serosa on the outside.
Describe smooth muscle
It still has actin and myosin, but no T-tubules, and loose SR throughout the sarcoplasm. There are no myofibrils and sarcomeres and thus no striations. The cells are small, single nucleated, and tapered at the ends.
How does smooth muscle have plasticity?
It can contract over a wide range of lengths. Important for stretchy organs: bladder, stomach, etc.
Visceral vs. multi-unit smooth muscle
Multiunit smooth muscle: each cell communicates with a nerve. Example in the eye.
visceral smooth muscle has gap junctions for communication between cells. There are also pacemaker cells in visceral smooth muscle.
Peristalsis
- circular muscles contract behind bolus
- longitudinal muscles ahead of the bolus contract
- contraction in circular muscle layer forces bolus forward
What is segmentation?
Rhythmic contractions to break up food. It is without any directional movement. Found in the sections of the small and large intestine.
three mechanisms that regulate and control digestion
- local factors (these are the primary stimulus for digestive activities; includes pH, distortion, presence of chemicals)
- neural control (short and long reflexes; sometimes called myenteric reflexes)
- hormonal control (18 hormones produced by enteroendocrine cells)
What are some local factors?
pH, physical distortion, chemicals (nutrients)
Functions of GI
ingestion mechanical processing digestion secretion absorption compaction, defecation
Look at mouth anatomy
page 839-841
how many deciduous teeth do kids have?
20: five on each side upper and lower
Describe the dental formula
#incisors, #canines, #premolars, #molars (for one side) All written like a fraction over the same for the bottom
What are the three phases of swallowing (deglutition)?
- buccal phase
- pharyngeal phase
- esophageal phase
Describe the buccal phase
it is the only voluntary step until defecation.
The bolus gets compressed against the hard palate. The tongue retracts, forces bolus to oropharynx. Soft palate elevates to seal the nasopharynx.
Describe the pharynx phase
tactile receptors get stimulated
swallowing center of MO is stimulated
Coordinated contraction of pharyngeal muscles
elevation of larynx and folding of esophagus.
bolus forced into esophagus
Describe the esophageal phase
it lasts 9 seconds. gets bolus to the lower esophageal sphincter.
Accumulation of too much serous fluid is called?
ascites
What does the greater and lesser omentum develop from in embryonic development? Falciform ligament?
Greater is from the dorsal mesentery of the stomach.
Lesser is from the ventral mesentery between stomach and liver.
Falciform ligament is from the ventral mesentery.
Capacity of stomach?
1-1.5 L.
What is chyme?
Food, saliva, gastric secretions. It is acidic and soupy.
There is a 3rd layer of muscle in the stomach. What is the third?
oblique muscle layer for mixing waves
Why is stomach epithelial cell turnover so high (3-7 days)?
acidic environment is very hard on cells.
Describe a gastric pit
These are open to the gastric surface. There are stem cells at the base, and each gastric pit communicates with several glands that stem from the lamina propria.
What are three cell types of the gastric glands?
- Parietal cells: make intrinsic factor to facilitate manufacture of HCl and absorption of B12
- G cells: secrete hormones
- Chief cells: secrete pipsinogen (gets converted to pepsin by HCL and is proteolytic), also secretes Renin and gastric lipase in infants.
How is HCl made by stomach?
Hydrogen ions are generated inside a partial cell. Carbonic anhydrase convert CO2 and H20 into carbonic acid, which dissociates. The bicarbonate ion gets ejected into IF and Cl gets passively imported into the cell. The Cl then diffuse out of the cell into the lumen of the gastric gland, as does the H+. Boom! HCl.
How is surface area maximized in the intestinal tract?
Circular folds (a permanent feature) and intestinal vili.
What is at the base of each vili?
intestinal glands and stem cells near the base of each gland. Each cell that is shed provides enzymes to the lumen
What is a lacteal?
A lymphatic vessl contained in a vilus. IT transports materials that can’t enter blood capillaries.
What increases the surface area of vili?
microvili
What are the areas of the abdomen?
The right hypochondriac region epigastric region left hypochondriac region right lumbar region umbilical region left lumbar region right inguinal region hypogastric region left inguinal region
Describe the segments of the small intestine
Duodenum (10 in)
mixing bowl of stomach, liver and pancreas, retroperitoneal
Jejunum (8.2 ft)
sharp bend, enters peritoneal cavity; most of the chemical digestion and nutrient absorption happens here
Ileum (11.5 ft)
Ends in ileocecal valve
Describe the cellular layers of the duodenum
D: fewer circular folds, small vili, receive chyme and neutralize acids.
Describe the cellular layers of the jejunum
J: numerous circular folds, long and abundant villi
Describe the cellular layers of the ileum
I: fewer circular folds, villi are stumpy, aggregated lymphoid nodules. They sample the bolus for pathogens
What kind of cells release the following hormones, and what stimulates their release?
- Gastrin
- Secretin
- GIP
- CCK
- VIP
- G-cells: stimulated by incompletely digested proteins
- S- cells: stimulated by chyme entering the duodenum
- K-cells: stimulated by fats and carbs, mostly glucose entering small intestine
- I-cells: triggered by lipids, partially digested proteins entering the duodenum
- Not known. stimulated by chyme int he duodenum
What is the action of:
- Gastrin
- GIP
- Secretin and CCK
- VIP
- acid production by parietal cells, stimulation of gastric motility, mixing waves
- inhibition of Gastrin; release of insulin from pancreas
- These cause release of pancreatic enzymes and buffers and bile secretion and ejection of bile from gallbladder
- Causes dilation of intestinal capillaries
What are the phases of gastric secretion?
cephalic phase, gastric phase, and intestinal phase.
What are the events at the cephalic phase?
Begins at the thought, smell or taste of food
Lasts for minutes
Vagus (parasympathetic) synapses at the submucosal plexus to stimulate the following:
mucous cells, chief cells, parietal cells, and G cells. They make Mucus, pepsinogen, HCl, and Gastrin, respectively.
What are the events at the gastric phase?
Begins when food arrives in the stomach. It lasts about 3-4 hours.
Chemoreceptors (increase in pH) and stretch receptors trigger this phase.
Gastrin stimulates contractions in the muscular external of the muscle and intestinal tract.
We still have stimulation of:
mucous cells (mucus)
Chief cells (pepsinogen)
parietal cells (HCl to pepsin via pepsinogen; in response to partially digested proteins)
The gastrin gets in the blood stream and further stimulates the chief cells and parietal cells
What are the events at the intestinal phase?
Begins when chyme enters the small intestine. Controls the rate of gastric emptying.
Here, stretch and chemoreceptors inhibit myenteric plexus and inhibit stomach mixing waves.
We also inhibit activity of chief cells, parietal cell and peristalsis.
Lipids and carbs entering the small intestine stimulate the production of CCK and GIP in duodenum.
What is the gastroenteric reflex?
stimulates motility and secretion along the small intestine
What is the gastroileal reflex?
triggers the opening of the illogical valve so things can get into the large intestine
Describe the large intestine and its major functions
About 5 ft long. absorbs water and compacts feces absorbs vitamins generated by bacterial functions Stores fecal matter includes cecum, colon, rectum
how does the large intestinal wall differ from other mucosa?
There aren’t any surface vili. The glands here don’t make enzymes, just mucus.
What causes the smell of feces?
indole and skatole (nitrogenous wastes), bacteria, hydrogen sulfide
Describe the reflexes of the rectum.
Stretch receptors from distention of the rectum cause stimulation of both a short reflex and a long reflex.
Short reflex: The stretch receptors stimulate myenteric plexus in sigmoid colon and rectum. This increases local peristalsis. Positive feedback loop until rectum is emptied.
Long reflex: Stretch receptors stimulate parasympathetic motor neurons in sacral spinal cord. These can do two things: 1. stimulate somatic motor neurons that lead to involuntary contraction of external anal sphincter (to prevent incontinence). 2. increases peristalsis throughout large intestine which causes increasing distention of the rectum in a positive feedback loop until bowel is emptied.
What are the accessory digestive organs? (4)
Salivary glands, gallbladder, pancreas, liver
What are the digestive and metabolic functions of the liver?
8 main functions, 6 other functions
- synthesizing and secreting bile
- storing glycogen and lipids
- Maintaining normal conenctrations of glucose, amino acids, and fatty acids in the blood stream.
- Synthesizing and interconverting nutrient types ( example carb to lipids)
- synthesizing and releasing cholesterol bound to transport proteins
- inactivating toxins
- storing iron
- Storing fat-soluable vitamins
Other:
- Synthesizing plasma proteins
- synthesizing clotting factors
- phagocytizing damaged red blood cells (Kupffer cells)
- Storing blood
- Absorbing and breaking down circulating hormones and immunoglobulins
- absorbing and inactivating lipid soluble drugs.
Which salivary glands contain amylase?
submandibular salivary glands
What is in the hepatic triad?
hepatic portal vein, hepatic portal artery, common bile duct
Describe the hepatic portal system
It is a venous system
Processes blood from the small intestine, spleen and pancreas before it reaches the heart
It basically has a “first pass” and can degrade drugs (good or bad)
Describe the process for storage and ejection of bile
- The liver continuously secretes bile
- as it remains in the gallbladder, it gets more concentrated
- release of CCK triggers ejection of bile into duodenum
- Bile salts break apart lipid droplets by emulsification
What are the enzymes secreted by the pancreas? (4)
pancreatic alpha-amylase
Pancreatic lipase
nucleases
proteolytic enzymes
Describe liver disease
If tissues of the liver degrade (cirrhosis), this can constrict blood flow. Possible causes include: viral hepatitis, alcoholism. Jaundice can occur when bilirubin is backed up into tissues. Portal hypertension causes distended vessels, varisces, which could rupture and cause fatal bleeding. When fluid from backed up venous blood is forced into peritoneal cavity, this is called ascites.
Gallstones form when?
Bile becomes too concentrated.
How does gastric band surgery lead to weight loss in an individual?
Stretch receptors are triggered much earlier than they normally would be, and the gastric phase of events starts early, signaling as if the stomach is full and digestion moves on from there.
